1. Field of Invention
The present invention relates to a method and apparatus for therapeutically focusing sonic or ultrasonic waves within a finite volume within an insonified medium. More particularly, the present invention relates to a method and apparatus for generating a plurality of standing waves which constructively intersect within a volume of target tissue within a human (or animal) body.
2. Description of the Prior Art
There are numerous known medical applications for which relatively high intensity sonic or ultrasonic waves may be advantageously used to induce various desired effects on the human (or other animal) body. Sonic and/or ultrasonic waves may be used, for example, to disrupt tissue and other materials, such as to break up kidney stones, blood clots or respiratory congestions. Sonic and/or ultrasonic waves may also be used to heat cancerous growths so as to make ionizing radiation treatment more effective. In addition, low-intensity sonic wave application is believed to facilitate healing.
Prior methods of introducing sonic and/or ultrasonic waves for medical treatment of the human body typically involve either applying the waves to the entire body, for example by immersing the body in an ultrasonic bath, or by localized vibration via a catheter, probe or similar instrument.
There are several problems associated with prior methods and apparatus of applying sonic and/or ultrasonic waves to the human body. When vibrational waves are applied, for example, through a catheter, the character of the applied vibrations (i.e. the location, the intensity, interaction with the vibrating medium, etc.) is limited due to the inherently small size of the catheter, or by the location of the blood vessel into which the catheter is to be inserted.
Also, because some prior means of applying sonic waves to the human body for medical treatment involve making an incision through, against or into which a vibrating member must be inserted, access may be limited by the damaged region in the vicinity of the incision, and there is an increased risk of infection associated with such methods.
Another problem with prior means of applying sonic waves to the human body for medical treatment is the collateral damage or effect that the waves may cause to areas of the body adjacent to or beyond the intended target tissue.
A problem associated with prior means of applying sonic waves to the human body for medical treatment involving vibrating probe members is that, because such probes are typically very small, the amount of power which can be applied with the probe is correspondingly limited. In addition, such probes also may directly damage areas of the body surrounding the target tissue.
As will be described more fully hereinbelow, an apparatus constructed in accordance with the present invention establishes a plurality of standing sonic waves within a patient's body to produce a therapeutic effect upon a target volume of tissue. Prior methods and apparatus for generating standing waves in media typically employ a single vibrator mechanism which imparts a coherent wave into a medium. The wave thus produced propagates through the medium until it encounters a substantially stationary reflective surface off of which the wave bounces directly back toward its source. A standing wave may be produced in this manner by adjusting the distance between the vibration source and the reflective surface to an integer multiple of the wavelength of the vibration. A problem with such transmitter-reflector methods of establishing standing waves is that the (single) transmitter has to emit vibrations of high enough intensity and of high enough quality to travel all the way from the emitter to the reflector and then back to the emitter.